[Alternative complement pathway activation by anti-band 3 antibodies].

Naturally occurring antibodies against the anion exchange protein of red cells (band 3 protein) can elicit in whole serum a strong C3b deposition to red cells under conditions which favor alternative complement pathway activation. Such a mode of opsonization calls for generation of an alternative C3 convertase nucleated by C3b covalently bound to anti-band 3. Senescent, but not young, red cells should also carry "C3b-anti-band 3" complexes, if clearance of in vivo aged red cells occurred by the same mechanism. We succeeded in isolating covalently linked complexes of C3b and IgG primarily from membranes of senescent red cells.